Can you buy a SIM in stores, no strings attached?

I wanted to add a family member onto my Magenta plan. It's not hard. I have a phone. All I needed was to pick up a SIM card. In Walmart, Walgreens, CVS I could find SIMs for every other company but nothing from T-Mobile. I went into a T-Mobile store the rep snarkily said "we don't do that here" (no customers in the store either).

Defeated, I went to the website to buy a SIM and their ordering system was down. Eventually it worked, and to their credit, the SIM is free online. But I could have driven to the store faster than it takes their Javascript to load and got my relative up-and-running today. And no I don't want to pay a $30 support-assist fee for someone to do what I can do myself.

I assume people hunting for SIM cards are looking for prepaid 95% of the time and T-Mobile would rather they go to MetroPCS, of which I could find plenty of SIMs.